Carbon-doped TiO2 Photocatalysts Research Articles

Ni Underlayer Effect for the Structure Development and Visible Light Photocatalytic Efficiency of Carbon-Doped TiO2 Film

Abstract Photocatalytic treatment of contaminated aqueous solutions makes use of the specific interaction between photocatalysts and ultra-violet or visible light irradiation. This method belongs to the wider class of Advanced Oxidation Processes that generates reactive oxygen species (peroxides, superoxide, hydroxyl radical, singlet oxygen, etc.) and uses them for the non-selective oxidation of various organic and inorganic compounds. In THE current study magnetron sputtering technique was used to deposit carbon-doped TiO2 films which are known to have significant photocatalytic activity in the visible light spectra and can be used for the neutralisation of contaminated solutions. Structural properties of the as-deposited films were analysed by XRD, XPS and AFM techniques, whereas their visible light photocatalytic activity was estimated by analysing Rhodamine B solution bleaching kinetics. When carbon-doped TiO2 photocatalysts were formed on borosilicate glass XRD analysis showed that they consisted of mixed phase (rutile-anatase) TiO2 where both phases contributed by similar parts. However, when the same deposition procedure was used to deposit carbon-doped TiO2 films on glass covered by Ni layer, formation of metastable anatase phase was enhanced. Estimation of visible light photocatalytic activity of the films revealed that Ni underlayer had positive effect for the efficiency of Rhodamine B solution bleaching and it could be beneficial for the practical wastewater treatment systems. It was suggested that observed improvement was mainly achieved due to the structural changes of TiO2 crystal phase, but other mechanisms like prevention of impurity diffusion from the glass substrate to the carbon-doped TiO2 film, or positive Ni doping effect could not be excluded completely.

Photodegradation of aqueous eosin yellow dye by carbon-doped TiO2 photocatalyst

In this study, a novel photocatalyst, carbon-doped TiO2 was prepared via a sol-gel technique with titanium (III) chloride as a precursor. The characterization of C-doped TiO2 was obtained by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and BET surface area analyses. The prepared catalyst’s photocatalytic activity was investigated using UV irradiation for the photo-oxidation of eosin yellow (EY) dye. The photocatalysis of EY dye was performed under various experimental parameters such as solution pH and oxidant dosage (H2O2). The prepared photocatalyst dosages were also taken separately to optimize process efficiency. About 77.43% of EY decolorization was obtained at an optimum pH of 3, and the performance was also observed by varying the oxidant concentration ranging from 5-10 mM. The % decolorization was higher for C-doped TiO2-200 photocatalyst (81.88%) compared to carbon-doped TiO2-400 photocatalyst (75.55%). It can be concluded that the carbon-doped TiO2, calcined at 200°C, can effectively decolorize EY dye in an aqueous medium.

Degradation of 2-Nitrophenol by Dielectric Barrier Discharge System: The Influence of Carbon Doped TiO2 Photocatalyst Supported on Stainless Steel Mesh

This study investigated the degradation of 2-nitrophenol (2-NP) in aqueous solution by dielectric barrier discharge (DBD) system alone and its combination with supported TiO2 photocatalysts. The TiO2 photocatalyst supported on a stainless steel mesh was synthesised using sol–gel solution of 8% polyacrylonitrile (PAN)/dimethylformamide/TiCl4 followed by pyrolysis in the furnace under N2 atmosphere at temperatures of 300, 350, or 400 °C for 3 h holding time. The supported catalysts were characterized for their morphologies, functional groups, crystallinity, surface areas and elemental chemical states by high resolution scanning electron microscope (HRSEM), Fourier transform infrared, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, and X-ray photoelectron spectroscopy. The influence of solution pH on the degradation of 2-NP was investigated. The residual concentration of 2-NP and the intermediate compounds were quantified and identified using high-performance liquid chromatography coupled with mass spectrometry (HPLC–MS). The concentration of the dissolved ozone, hydrogen peroxide and hydroxyl radicals generated by the DBD in the presence or absence of a catalyst was monitored using ultraviolet–visible spectroscopy and photoluminescence spectroscopy. The HRSEM, HRTEM, XRD and BET analysis revealed that the optimal thermal conditions to obtain well supported uniformly grown, highly active crystalline TiO2 catalysts with high specific surface area was 350 °C at a 3 h holding time in N2 atmosphere with a flow rate of 20 mL/min. The supporting procedure simultaneously carbon doped the photocatalyst. The DBD system alone without catalysts successfully mineralised 58.6% of 2-NP within 60 min while combined DBD/supported TiO2 nanocrystals achieved 77.5% mineralisation within the same treatment time. The increase in mineralisation rate was attributed to the existence of a synergistic effect between the DBD system and the supported catalysts. 2-NP degradation proceeded via hydroxylation, nitration and denitration using DBD alone and combined DBD/Supported TiO2 photocatalyst. Catechol, hydroquinone, hydroxyl-1,4-benzoquinone, 2-nitrohydroquinone, and 2,4-dinitrophenol were identified as major intermediate products. The order of production of free reactive species by DBD alone and combined DBD with supported photocatalyst was OH° > H2O2 > O3.The results showed that the combined system was more than effective than DBD alone for the degradation of the 2-NP in aqueous solution.

Synthesis and characterization of carbon doped TiO2 photocatalysts supported on stainless steel mesh by sol-gel method

This study synthesized pure anatase carbon doped TiO₂ photocatalysts supported on a stainless steel mesh using a sol-gel solution of 8% polyacrylonitrile (PAN)/dimethylformamide (DMF)/TiCl₄. The influence of the pyrolysis temperature and holding time on the morphological characteristics, particle sizes and surface area of the prepared catalyst was investigated. The prepared catalysts were characterized by several analytical methods: high resolution scanning electron microscopy (HRSEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS). The XRD patterns showed that the supported TiO₂ nanocrystals are typically anatase, polycrystalline and body-centered tetragonal in structure. The EDS and XPS results complemented one another and confirmed the presence of carbon species in or on the TiO₂ layer, and the XPS data suggested the substitution of titanium in TiO₂ by carbon. Instead of using calcination, PAN pyrolysis was used to control the carbon content, and the mesoporosity was tailored by the applied temperature. The supported TiO₂ nanocrystals prepared by pyrolysis at 300, 350, and 400oC for 3 h on a stainless steel mesh were actual supported carbon doped TiO₂ nanocrystals. Thus, PAN/DMF/TiCl₄ offers a facile, robust sol-gel related route for preparing supported carbon doped TiO₂ nanocomposites.

Microbial inactivation kinetics and mechanisms of carbon-doped TiO2 (C-TiO2) under visible light

In this study, titanium dioxide nanoparticles doped with carbon (C-TiO2) were synthesized by means of sol–gel methods, and the synthesis was verified by means of X-ray photoelectron spectroscopy. The nanoparticles’ photocatalytic disinfection activity of Listeria monocytogenes was tested under UV and visible light. The observed inactivation levels for 150min of visible light exposure with and without UV cutoff filters were 2.10 and 2.45 log, respectively. We also found that traditional reactive oxygen species had insignificant actions on C-TiO2 photocatalysts and that L. monocytogenes inactivation in the C-TiO2 system under visible light was induced in large part by the midgap states (hmid+) that was produced photochemically from the visible light response. C-TiO2 was found to accelerate bacterial inactivation (of L. monocytogenes) in the presence of visible light. Our data suggests that the C-TiO2 may be useful in the development of alternative disinfectants for environmental applications.

Synthesis of high visible light active carbon doped TiO2 photocatalyst by a facile calcination assisted solvothermal method

The carbon doped TiO2 powders have been successfully prepared by a facile calcination assisted solvothermal method using titanium tetra-n-butoxide or TiCl3 together with ethanol as starting materials without the addition of any other extra carbon sources. The physicochemical properties of as-synthesized samples were characterized by the X-ray diffraction, Fourier transform-infrared spectroscopy, UV–vis diffuse reflectance spectroscopy, BET specific surface area, and X-ray photoelectron spectroscopy. Besides, the effects of post solvothermal reaction heating temperature and raw materials on the carbon doping in TiO2 have been investigated. The experimental results showed that carbon has been doped into TiO2 lattice by replacing the oxygen site with the production of oxygen vacancy. In addition, carbon doped TiO2 samples exhibited not only very good destruction ability of NO gas but also excellent degradation ability of methyl orange solution under the visible light much superior to P25 and N–TiO2. The employed method in this work provided a favorable evidence that the effect of carbon doping on the properties of samples should be taken into consideration when preparing TiO2 based photocatalyst by a hydrothermal or solvothermal method with the assist of calcination.

Preparation of a visible sensitive carbon doped TiO2 photo-catalyst by grinding TiO2 with ethanol and heating treatment

We have synthesized a carbon doped titanium oxide powder (C-TiO2) which is a photo-catalytic material acting under irradiation of light of wave length in visible region, by mechanochemical (MC) and heating operations. The MC operation is conducted by grinding TiO2 with ethanol (C2H5OH) in air, and the heating is carried out at different temperatures in air. The prepared samples were characterized by a series of analytical methods including X-ray diffraction, thermogravimetry-mass spectroscopy, Fourier transform infrared spectroscopy, specific surface area measurement, X-ray photoelectron spectroscopy (XPS), NOx gas decomposition and ultraviolet visible spectroscopy (UV–vis). XPS analysis particularly demonstrates the existence of C–Ti and C–O bindings, to which the improvement in photo-catalyst is attributed.